RF communication systems having a plurality of transmitter sites are well known. An example of such a system, of course, is a cellular radio system. Such a system is depicted in FIG. 1. There is shown a cellular radio system 100 having a plurality of transmitter sites, as in the prior art. Although FIG. 1 only depicts two such transmitter sites, 111 and 131, it will be appreciated that the actual number of sites will vary from system to system.
Referring now to transmitter site 111, a common base station 105 is coupled to a digital radio interface module 115 via link 113. The digital radio interface module 115, in turn, is coupled to a radio control unit module 119 via link 117. The radio control unit module 119, in turn, is coupled to an antenna 121.
Referring now to transmitter site 131, the common base station 105 is coupled to a digital radio interface module 135 via link 133. The digital radio interface module 135, in turn, is coupled to a radio control unit module 139 via link 137. The radio control unit module 139, in turn, is coupled to an antenna 141.
Typically the links 117 and 137 are implemented using fiber optic cables. Also, typically these links are arranged as ISO layer 2 HDLC data links.
Referring still to FIG. 1, those skilled in the art will appreciate that the remote radio control unit modules 119 and 139 must be synchronized to a common clocking source in the common base station 105. There are several ways to distribute clocking information to the remote sites. One way would be to run additional fiber optic facilities from the serving digital radio interface modules. The problem with this approach is the added cost for providing the additional fiber optic link for each transmitter site. Considering the length of each link and the total number of sites, this approach may prove expensive.
As a result, it would be desirable to arrange each individual data link to transport the needed synchronization information along with the data information transported by the HDLC protocol.